Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$112.92	6.731%	$120.5206	$120.52	$120.50	$120.50
Purchase #2	$176.72	12.762%	$199.273	$199.27	$199.25	$199.30
Purchase #3	$123.80	11.725%	$138.3156	$138.32	$138.30	$138.30
Purchase #4	$146.82	5.426%	$154.7865	$154.79	$154.80	$154.80
Purchase #5	$55.56	5.215%	$58.4575	$58.46	$58.45	$58.50
Purchase #6	$214.75	4.555%	$224.5319	$224.53	$224.55	$224.50
Purchase #7	$228.71	11.519%	$255.0551	$255.06	$255.05	$255.10
7 purchase totals =	$1,059.28		$1,150.9402	$1,150.95	$1,150.90	$1,151.00